Flow sensor

ABSTRACT

A parallel flow sensor, of the type in which a sensing jet flows parallel to and within a measured flow and experiences velocity variations as a linear function of the measured flow, is modified to vary the sensing jet velocity cosinusoidally in response to angular variations in the measured flow. The flow sensor is located in a flow alignment tube, each end of which has a truncated cone flaring outwardly therefrom in axial alignment with the tube. The truncated cone is spaced from the tube end by angularly spaced supporting ribs which also serve as flow guides along the interior surface of the truncated cone. A short length of cylindrical tubing, having a smaller diameter than the flow alignment tube, is also supported by the ribs and extends from the interior of the flow alignment tube through one end of the truncated cone. Two orthogonally oriented sensors of this type provide respective output pressures which represent the rectangular co-ordinates of a measured flow such as wind.

United States Patent [1 1 Neradka 1 Oct. 30, 1973 i 1 FLOW SENSOR [75]Inventor: Vincent F. Neradka, Rockville, Md.

['73] Assignee: Bowles Fluidics Corporation,

Silver Spring,

[22] Filed: Dec. 3, 1971 [21] Appl, No.: 204,448

Primary Examiner-Richard C. Queisser Assistant Examiner-John P.Beauchamp Attorney-Howard L. Rose 57] ABSTRACT A parallel flow sensor,of the type in which a sensing jet flows parallel to and within ameasured flow and,

experiences velocity variations as a linear function of the measuredflow, is modified to vary the sensing jet velocity cosinusoidally inresponse to angular variations in the measured flow. The fl-ow sensor islocated in a flow alignment tube, each end of which has a truncated coneflaring outwardly therefrom in axial alignment with the tube. Thetruncated cone is spaced from the tube end by angularly spacedsupporting ribs which also serve as flow guides along the interiorsurface of the truncated cone. A short length of cylindrical tubing,having a sinaller diameter than the flow alignment tube, is alsosupported by the ribs and extends from'the interior of the flowalignment tube through one end of the truncated cone. Two orthogonallyoriented sensors of this type provide respective output pressures whichrepresent the rectangular coordinates of a measured flow such as wind.

11 Claims, 4 Drawing Figures PATENTED UN 30 I975 INVENTOR V\NCENT F.NERQDKA BY FWW (i (9% C. Edflfil FLOW SENSOR BACKGROUND OF THE INVENTIONThe invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment to us of any royalty thereon.

The present invention relates to flow sensing and, more particularly toa flow sensor having no moving parts and which is suitable for use as atwo-axis or three-axis wind sensor.

Fluidics technology has produced some uniquely advantageous approachesto measuring flow, primarily because of the fact that fluidic elementsrequire no moving parts. One example of a prior art fluidic flow sensoris found in U.S. Pat. No. 3,343,413 to South et al. The South et alsensor has become known as a crossflow sensor wherein a fluid jet isissued generally perpendicular to the measured flow and is deflectedrelative to a receiver by the measured flow. The jet pressure receivedat the receiver is a function of measured flow velocity. The cross-flowsensor can be utilized as a two-axis wind sensor providing fourappropriately spaced receivers for the sensing jet, the sensing jetpressure as received at each receiver providing a measure of arespective rectangular co-ordinate of the wind.

The major disadvantage of the cross flow sensor is its limited range.Specifically, the sensing jet supply pressure and receiver positions canbe adjusted to provide effective measurement only over a limited rangeof measured flow. If the measured flow is too low, jet deflection is notperceived by the receivers; if the mea sured flow is too high the jet isdeflected beyond the reception area of the receivers.

Another disadvantage of the cross-flow sensor is nonlinearity of itsoutput pressure versus measured flow characteristic. Specifically,unless the supply pressure is high, the mechanism of the units operationis momentum interaction which is characteristically nonlinear withvelocity.

The aforementioned disadvantages of the cross-flow sensor weresubstantially eliminated by the development of the parallel-flow sensor.The latter is the subject of U.S. Pat. No. 3,705,534 to Ture'k. Theparallelflow sensor utilizes a sensing jet issued parallel to and withinthe measured flow. The velocity of the jet is augmented or diminished bythe measured flow, and the resulting jet pressure at the receiver is alinear function of the measured flow over a wide range of flow. When twooppositely directed power jets are issued within the same measured flow,the differential pressure appearing across their receivers is linearover an even greater flow range.

The aforementioned Turek patent describes a twoaxis wind sensoremploying two orthogonally oriented parallel flow sensors disposed inrespective flowaligning tubes. One of the sensors is utilized to measurewind magnitude; the other measures wind direction. The output pressureof the direction sensor is employed as an error signal for a servomotorwhich rotates the assembly until the direction sensor output pressure isnulled. At this position the direction sensor is perpendicular to theprevalent wind direction and the magnitude sensor is parallel to theprevalent wind direction. Wind magnitude can thus be easily recordedas'a linear function of the output pressure of the magnitude sensor;wind direction is measured by the angular position of the assembly. Theprimary disadvantage of this approach to two-axis wind sensing is thenecessity for moving parts to position the assembly according to winddirection. These moving parts, in effect, nullify the primary advantageof utilizing fluidics, namely the absence of failure-prone moving parts.Also, extension of this approach to three-axis measurement is difficult.

It is therefore a primary object of the present invention to provide atwo-axis wind sensor employing fluidic technology and which does notrequire moving parts.

A preliminary approach to solving the stated problem would appear to bethe utilization of two orthogonally oriented parallel-flow sensors,located in respective flow-aligning tubes as above. Instead of utilizinga wind direction-controlled servo-motor, however, the assembly would befixed and the output pressures of each sensor would represent arespective rectangular or cartesian component of the measured wind.These pressures could then be converted to the conventionally requiredpolar coordinate system by suitable resolver circuits. The rationalebehind this approach resides in the fact that the effective entrancearea for the flowaligning tube varies cosinusoidally with the angulardisplacement between the tube axis and the wind direction. Consequentlythe flow through the tube should vary cosinusoidally with winddirection. According to this rationale, therefore, the output pressuresfrom the two orthogonally oriented sensors would be Rcos0 and RsinO,respectively, where R is the magnitude of the wind and 6 is the anglebetween the axis of the first sensor and the wind direction. Thesecomponents are easily converted to polar coordinates.

Unfortunately, however, the output pressure of the parallel flow sensordoes not follow the wind direction in a cosinusoidal manner. Afterconsiderable investigation it was found that flow separation at the endsof the tube was the cause of some erratic output pressures from thesensor, particularly when the wind direction was within i 20 of beingperpendicular to the tube axis. I

It is therefore an object of the present invention to modify theparallel flow sensor to achieve a cosinusoidal variation of outputpressure with input flow direction. 1

It is another object of the present invention to. provide a two-axis orthree-axis flow sensor employing two parallel flow sensors having outputpressures which are linear functions of the rectangular or cartesiancomponents of the measured flow.

SUMMARY OF THE INVENTION According to the principles of the presentinvention, each end of both orthogonally-oriented flow-aligning tubesincludes angularly spaced supporting ribs proj'ecting therefrom. Theouter edges of the ribs support a truncated conical member which flaresoutwardly from the tube and is axially aligned. therewith. The ribs areextended along the interior surface of the truncated conical member toserve as flow guides. The inner edges of the ribs support a shortcylindrical member of smaller diameter than the flow-aligning tube. Thecylindrical member is coaxial with the tube and extends from within .thetube to the interior of the conical member. Depending upon the flareangle of the truncated conical member, the spacing between the flowaligning tube ad the conical member, and orientation of the supportingribs, a reasonably accurate cosinusoidal characteristic of outputpressure versus flow direction can be obtained. Two orthogonallyoriented flow sensors, thusly modified, provide rectangular co-ordinatesof measured wind with sufficient accuracy for all practical purposes.

BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects,features and advantages of the present invention will become apparentupon consideration of the following detailed description of specificembodiments thereof, especially when taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a partially cut-away view in perspective of a twoaxis windsensor constructed according-to the principles of the present invention;

FIG. 2 is an end view of one of the sensors of FIG. 1;

FIG. 3 is a view in perspective of an insert employed at each end of thesensors of FIG. 1; and

FIG. 4 is a view in section taken along lines 44 of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring specifically to FIG. 1 ofthe accompanying drawings, a pair of flow alignment tubes and 11 aremounted in mutually orthogonal relationship. Specifically, when the unitof FIG. 1 is employed as a wind sensor, tubes 10 and 11 are disposedhorizontally, with one tube in north-south alignment and the other ineast-west alignment. Inside each tube, although only the interior oftube 10 is illustrated in FIG. 1, there is disposed a parallel flowsensor of the type described in the above referenced Turek patent. Thedifferential pressure version of the parallel flow sensor isillustrated, although the single-ended embodiment may be similarlyemployed. The parallel flow sensor includes a manifold 13 which receivespressurized fluid, for example pressurized air, and distributes same totwo oppositely directed nozzles 15 and 17. Both nozzles'15 and 17 arepositioned to issue sensing streams of the pressurized fluid in adirection parallel to the longitudinal axis of flow alignment tube 10. Areceiver tube 19 is positioned to receive the sensing stream from nozzle15 but is located to receive a portion of the sensing stream lyingoutside the constant velocity core. Wind flowing through tube 10viscously interacts with the=sensing stream to either retard or augmentthe sensing jet velocity, depending upon which direction the wind flowsthrough the tube Consequently the pressure in receiver tubes 19, astransmitted to output passage 20, is a measure of the velocity of thewind flowing through tube 10.

A similar receiver 21 is positioned to receive the sensing stream issuedby nozzle 17 and transmits a pressure proportional to wind velocity tooutput passage 22. Assuming equal jet dynamic pressures at receivers 19,21 with no wind in tube 10, the differential pressure between thereceivers varies linearly with wind velocity through the tube. The mainadvantage of this differential pressure approach resides in the factthat any nonlinearities in the individual pressures are balanced and ahighly linear output signal versus wind velocity is the result.

At each end of both of tubes 10 and 11 there is disposed a truncatedcone 25, spaced from the tube end and coaxial with the longitudinal axisof the tube. The

truncated cone entrance assembly is best illustrated in FIGS. 2, 3 and4.

Four supporting ribs 26 are disposed at each end of tubes 10 and 11 andare spaced at intervals. The relatively thin outer edge of each rib 26is secured to the interior wall of the flow alignment tube. Each ribextends width-wise radially inward toward the longitudinal axis of theflow-alignment tube. Each rib also extends length-wise longitudinallyout of the flow alignment tube and then bends at approximately 45 in aradially outward direction. Truncated cone 25 is supported by theradially outward bent portion of ribs 26, with the inner surface oftruncated cone 25 secured to the outer edge of ribs 26. Truncated cone25 flares outwardly away from the flow-alignment tube V and is spacedtherefrom.

A small cylinder 27 has its longitudinal axis disposed coaxial with thelongitudinal axis of the flow alignment tube. The outer wall of cylinder27 is secured to the radially inward edge of each of the four ribs 26. Aportion of cylinder 27 extends out of the flow alignment tube andslightly past the truncated end of truncated cone The flow separationproblem, which drastically distorts the cosinusoidal output pressureversus wind direction characteristic of the sensor when there is nomodification of the end of flow tubes 10 and 11, is controlled by theassembly described above in conjunction with truncated cone 25. Windflow along both surfaces of the truncated cone acts to control theseparation problem much in the same manner that slotted flaps onairfoils control separation of flow from the foil surface. Specifically,the slots in a flap act to direct bypass air from the lower surface tothe top surface of the foil to move the point of flow separation fromthe top surface downstream. If the space between truncated cone 25 andthe end of tube 10 (or 11) is considered as a slot in an airfoil flap,the same principle applies, whereby bypass air from the outer surface ofthe truncated cone acts to delay separation of flow from the innersurface of the truncated cone and from the inner surface of the flowalignment tube.

The unit as described provides two differential pressure signals, onefrom each sensor. These two signals correspond to the rectangularco-ordinate components of the wind or flow being measured. For example,if the direction from left to right along the longitudinal axis of tube10 is considered a reference direction, the differential pressuremeasured by the sensor in tube 10 may be expressed as RcosO, where R isthe actual wind or flow magnitude, and 6 is the angular displacement ofwind direction from the reference direction. The differential outputpressureat tube 11 is similarly expressed as Rsin6. To convert theserectangular co-ordinate components into polar co-ordinates ('i.e.,magnitude and direction), the individual differential pressures may beconverted to respective voltages in respective pressure to voltagetransducers. The resulting voltages may then be fed to a suitableresolver circuit'which converts rectangular co-ordinate components intopolar components. Such a resolver, for example, would be the Rectangularto Polar Converter, 695 Series, manufactured by Transmagnetics, Inc. ofF armingdale, New York. Such a resolver receives signals Rsin6 and RcosOin voltage form and provides output voltages proportional to R and 0.

The basic output pressure wind direction characteristic of the parallelflow sensor as modified according to the present invention issufficiently close to cosinusoidal for substantially all practical windmeasurements. Standard wind direction measurements are usually taken interms of standard compass point subdivisions which are typically 1 125or 22.5 apart. The accuracy of the present invention far exceeds theaccuracy required for such measurements.

Typical dimensions for the components of the tube entrance assembly aregiven in the table below by way of example:

Inside diameter of tube -1 A in.

Length of truncated cone 25-341 in.

Inside diameter of truncated cone entrance2 A in. Inside diameter oftruncated cone exit'1 A in.

Space between truncated cone exit and tube l0 /2 Inside diameter ofcylinder 27-% in.

Angle between tube axis and cone wall45 The dimensions listed above canvary, particularly if the size of tubes 10 and 11 are changed. By andlarge,

the correct relative dimensions for different sizes of.

tubes 10 and 11 are found empirically.

The number of ribs 26 need not be four, but can be more or less.Similarly, the angle of the truncated cone can be varied within thescope of this invention. The important point is to provide a truecosinusoidal wind direction versus output pressure characteristic, andto do this the various components of the present invention can be sizedaccordingly.

As mentioned above, the principles of the present invention are readilyadapted to three-axis flow sensing. Specifically, a third sensor,orthogonally disposed relative to flow tubes 10 and 11, may be utilizedto monitor flow in still a third direction.

While I have described and illustrated specific embodiments of myinvention, it will be clear that variations of the details ofconstruction which are specifically illustrated and described may beresorted to without departing from the true spirit and scope of theinvention as defined in the appended claims.

I claim:

1. In a flow sensor of the type in which measured flow of variabledirection is conducted through. a flowalignment tube having at least oneentrance, an improvement for rendering the flow through said tube asubstantially cosinusoidal function of the direction of the measuredflow relative to the longitudinal axis of said tube, said improvementbeing characterized by:

a truncated cone having a relatively wide ingress end opening and arelatively small egress end opening; and

means for supporting said truncated cone proximate to but spaced fromsaid tube entrance, coaxial with said tube, and with the egress endopening of said truncated cone closer to said tube than said ingress endopening.

2. The combination according to claim 1 wherein the diameter of theegress end opening of said truncated cone is approximately equal todiameter of the said tube entrance.

3. The combination according to claim 1 wherein 6 said meansforsupporting comprises a plurality of I'lb members secured to andprojecting outwardly from the entrance to said tube, said ribs flaringoutwardly from said entrance along the interior surface of saidtruncated cone.

4. In a flow sensor of the type in which measured flow of variabledirection is conducted through a flowalignment tube having at least oneentrance, an improvement for rendering the flow through said tube anaccurate cosinusoidal function of the direction of the measured flowrelative to the longitudinal axis of said tube, said improvement beingcharacterized by:

a truncated cone having a relatively wide ingress end opening and arelatively small egress end opening; and

means for supporting said truncated cone proximate to but spaced fromsaid tube entrance, coaxial with said tube, and with the egress: endopening of said truncated cone closer to said tube than said ingress endopening;

wherein said means for supporting comprises a plurality of rib memberssecured to and projecting outwardly from the entrance to said tube, saidribs flaring outwardly from said entrance along the interior surface ofsaid truncated cone;

and further comprising a relatively short cylindrical member disposedconcentrically within said tube and projecting outward from said tubeentrance to at least the open egress end of said truncated cone, thediameter of said cylindrical member being smaller than the diameter ofthe open egress end of said truncated cone.

5. The combination according to claim 4 wherein the outer wall of saidcylindrical member is secured to the radially inner edges of said ribmembers.

6. In a parallel flow sensor of the type comprising at least one sensingjet flowing within a flow alignment tube, and a receiver located in saidtube for receiving said jet at a presssure which varies with the speedof measured flow in said tube, an improvement for rendering the pressurereceived by said receiver a cosinusoidal function of the direction ofsaid measured flow before entering said tube, the improvementcharacterized by:

a plurality of ribs projecting outwardly from one end of said tube andspaced at equal angular locations, said ribs flaring radially outwardfrom beyond said one end .of said tube; and

a truncated conical member, open at both ends and having its interiorsurface secured to the radially outward edges of said ribs, the radiallysmaller end of said member being spaced from said tube but closerthereto than the radially larger end of said member.

7. In a parallel flow sensor of the type comprising at least one sensingjet flowing within a flow alignment tube, and a receiver located in saidtube for receiving said jet at a pressure which varies with the speed ofmeasured flow in said tube, an improvement for rendering the pressurereceived by said receiver an accurate cosinusoidal function of thedirection of said measured flow before entering said tube, theimprovement characterized by:

a plurality of ribs projecting outwardly from one end of said tube andspaced at equal angular locations, said ribs flaring radially outwardfrom beyond said one end of said tube;

a truncated conical member open at both ends and having its interiorsurface secured to the radially outward edges of said ribs, the radiallysmaller end of said member being spaced from said tube but closerthereto than the radially larger end of said member; and

a cylinder of relatively short length and diameter locatedconcentrically within said tube and projecting outwardly from said oneend to at least the radially smaller end of said member, the outer wallof said cylinder being secured to the radially inner edges of said ribs.

8. The combination according to claim 7 wherein the diameter of saidradially smaller end of said member is no larger than the diameter ofsaid tube and larger than the diameter of said cylinder.

9. The combination according to claim 8 further comprising a secondtruncated conical member, a second plurality of said ribs, and a secondcylinder, all disposed at the opposite end of said tube from said oneend and arranged in the same manner as at said one end.

10. The combination according to claim' 9 further comprising a secondflow alignment tube having an interior parallel flow sensor inside and atruncated conical member, a plurality of ribs, and a cylinder at eachend, all arranged in an identical manner to that in the first-recitedflow alignment tube, said two flow alignment tubes being oriented withtheir longitudinal axes mutually perpendicular.

11. The combination according to claim 10 wherein said parallel flowsensors in said flow alignment tubes each comprise means for issuing twooppositely directed sensing jets and means for receiving said jets as adifferential pressure proportional to flow through the tube. he tube.

1. In a flow sensor of the type in which measured flow of variable direction is conducted through a flow-alignment tube having at least one entrance, an improvement for rendering the flow through said tube a substantially cosinusoidal function of the direction of the measured flow relative to the longitudinal axis of said tube, said improvement being characterized by: a truncated cone having a relatively wide ingress end opening and a relatively small egress end opening; and means for supporting said truncated cone proximate to but spaced from said tube entrance, coaxial with said tube, and with the egress end opening of said truncated cone closer to said tube than said ingress end opening.
 2. The combination according to claim 1 wherein the diameter of the egress end opening of said truncated cone is approximately equal to diameter of the said tube entrance.
 3. The combination according to claim 1 wherein said means for supporting comprises a plurality of rib members secured to and projecting outwardly from the entrance to said tube, said ribs flaring outwardly from said entrance along the interior surface of said truncated cone.
 4. In a flow sensor of the type in which measured flow of variable direction is conducted through a flow-alignment tube having at least one entrance, an improvement for rendering the flow through said tube an accurate cosinusoidal function of the direction of the measured flow relative to the longitudinal axis of said tube, said improvement being characterized by: a truncated cone having a relatively wide ingress end opening and a relatively small egress end opening; and means for supporting said truncated cone proximate to but spaced from said tube entrance, coaxial with said tube, and with the egress end opening of said truncated cone closer to said tube than said ingress end opening; wherein said means for supporting comprises a plurality of rib members secured to and projecting outwardly from the entrance to said tube, said ribs flaring outwardly from said entrance along the interior surface of said truncated cone; and further comprising a relatively short cylindrical member disposed concentrically within said tube and projecting outward from said tube entrance to at least the open egress end of said truncated cone, the diameter of said cylindrical member being smaller than the diameter of the open egress end of said truncated cone.
 5. The combination according to claim 4 wherein the outer wall of said cylindrical member is secured to the radially inner edges of said rib members.
 6. In a parallel flow sensor of the type comprising at least one sensing jet flowing within a flow alignment tube, and a receiver located in said tube for receiving said jet at a presssure which varies with the speed of measured flow in said tube, an improvement for rendering the pressure received by said receiver a cosinusoidal function of the direction of said measured flow before entering said tube, the improvement characterized by: a plurality of ribs projecting outwardly from one end of said tube and spaced at equal angular locations, said ribs flaring radially outward from beyond said one end of said tube; and a truncated conical member, open at both ends and having its interior surface secured to the radially outward edges of said ribs, the radially smaller end of said member being spaced from said tube but closer thereto than the radially larger end of said member.
 7. In a parallel flow sensor of the type comprising at least one sensing jet flowing within a flow alignment tube, and a receiver located in said tube for receiving said jet at a pressure which varies with the speed of measured flow in said tube, an improvement for rendering the pressure received by said receiver an accurate cosinusoidal function of the direction of said measured flow before entering said tube, the improvement characterized by: a plurality of ribs projecting outwardly from one end of said tube and spaced at equal angular locations, said ribs flaring radially outward from beyond said one end of said tube; a truncated conical member open at both ends and having its interior surface secured to the radially outward edges of said ribs, the radially smaller end of said member being spaced from said tube but closer thereto than the radially larger end of said member; and a cylinder of relatively short length and diameter located concentrically within said tube and projecting outwardly from said one end to at least the radially smaller end of said member, the outer wall of said cylinder being secured to the radially inner edges of said ribs.
 8. The combination according to claim 7 wherein the diameter of said radially smaller end of said member is no larger than the diameter of said tube and larger than the diameter of said cylinder.
 9. The combination according to claim 8 further comprising a second truncated conical member, a second plurality of said ribs, and a second cylinder, all disposed at the opposite end of said tube from said one end and arranged in the same manner as at said one end.
 10. The combination according to claim 9 further comprising a second flow alignment tube having an interior parallel flow sensor inside and a truncated conical member, a plurality of ribs, and a cylinder at each end, all arranged in an identical manner to that in the first-recited flow alignment tube, said two flow alignment tubes being oriented with their longitudinal axes mutually perpendicular.
 11. The combination according to claim 10 wherein said parallel flow sensors in said flow alignment tubes each comprise means for issuing two oppositely directed sensing jets and means for receiving said jets as a differential pressure proportional to flow through the tube. 